Fluid isolator

ABSTRACT

A fluid isolator for use between a high-pressure fluid line and a low-pressure fluid line for actuating one of a plurality of operators from a common source of pressure fluid. Through first and second free-floating pistons mounted in first and second cylinders, power is transferred from a primary fluid circuit to a secondary fluid circuit to actuate the operator. A valving arrangement comprising a spool-type control valve actuated by a spool-type pilot valve is operable to direct high-pressure fluid alternately to the cylinders to drive the pistons through power strokes. The pilot spool is physically attached to the first piston so that the movement of the piston shifts the pilot spool to cause the control spool to shift. To accommodate changes in the volume of the fluid, herein hydraulic fluid, in the secondary circuit, the second cylinder is larger in volume than the first cylinder. In one embodiment, the pilot valve is formed concentric with the control valve, and the pilot spool slides within a central passage in the control spool.

United States Patent flonald K. Schaeve;

3,100,965 8/1963 Blackburn....................

[72] Inventors Edward Ashby both Rockhrd' Primary Examiner-Martin P.Schwadron [2]] Appl. No. 879,490 A E A M Z 22 Filed Nov. 24, 1969 f s'fp g s 8 J V & 0 Patented Nov. 30, 1971 norneyo e, u ar ey lg, oit sann[73] Assignee Barber-Coleman Company Rockfordv ABSTRACT: A fluidisolator for use between a high-pressure fluid line and a low-pressurefluid line for actuating one of a plurality of operators from a commonsource of pressure fluid. [54] FLUID ISOLATOR Through first and secondfree-floating pistons mounted in first 14 Claims, 6 Drawing Figs.

. and second cylinders, power IS transferred from a primary [52] U.S.fluid circuit to a secondary fluid circuit to actuate the opera- 60/51,91/46] .Fl5b 15/18,

tor. A valving arrangement comprising a spool-type control [5 l] lnt.valve actuated by a spool-type pilot valve is operable to directhigh-pressure fluid alternately to the cylinders to drive the pistonsthrough power strokes. The pilot spool is physically attached to thefirst piston so that the movement of the piston shifts the pilot spoolto cause the control spool to shift. To accommodate changes in thevolume of the fluid, herein hydraulic fluid, in the secondary circuit,the second cylinder is larger in volume than the first cylinder. in oneembodiment, the pilot valve is formed concentric with the control valve,and the pilot spool slides within a central passage in the controlspool.

8&3 33 m xx 1 4 new mm 7 77 63 33 F 1 11 mm m s I WM m .1 m9 W mm m1...M mm m n. mm W" m5 ME 36 u Tl fl In nA m m mT mh o m e m RwHR n n 4] N56U ww ll il 92 o l m M F n3 1 1 1 0 6 U U 23 FLUID ISOLATOR BACKGROUND OFTHE INVENTION This invention relates to a fluid isolator for use betweena high-pressure fluid line and a low-pressure line for actuating one ofa plurality of operators from a common source of pressure fluid. Toisolate the operator from the high-pressure line,

' two separate fluid circuits are used with the primary circuit beingconnected between the high-pressure line and the lowpressure line andthe secondary circuit, which is normally filled with hydraulic fluid,being connected to the operator to form a closed circuit. Two cylinderswith free-floating pistons join the circuits together for transmissionof power from the primary circuit to the secondary without thetransmission of fluid between the circuits. In the primary circuit, avalving arrangement with a valve member which moves between twopositions is operable to direct pressure fluid first to one cylinder andthen the other to drive the pistons through power strokes to cause aflow of hydraulic fluid in the secondary circuit. With this arrangement,the high-pressure fluid line is isolated from the operator so that, if aleak occurs in the secondary circuit, fluid does not escape from thehigh-pressure line and the latter is still able to service the otheroperators.

SUMMARY OF THE INVENTION The primary object of the present invention isto provide a valving arrangement which provides positive shifting of thevalve member between the positions to provide quiet, smooth, positive,functioning of the isolator during normal operation and which, upon leakoccurring in the secondary circuit stops the valve member in one of thepositions and holds it there thus providing a quiescent state of thevalve arrangement to prevent nonuseful expenditure of energy and damageto the parts of the isolator and to eliminate noise caused by movingparts.

It is another object to provide such a valving arrangement which iscapable of using either hydraulic or pneumatic pres sure fluid in theprimary circuit.

A further object of the invention is to provide a valving arrangementwhich is operable, when a leak occurs, to direct high-pressure fluid toboth cylinders to drive both pistons to the ends of their cylindersadjacent the secondary circuit and to connect the valving arrangement toone piston so that the valve member is fixed in its final position bythe final position of the one piston. More specifically, the valvingarrangement comprises a spool-type control valve with the spool beingthe valve element and a spool-type pilot valve to actuate the shiftingof the control spool, and the pilot spool is physically con- 7 nected tothe one piston so that the spool is physically connected to the onepiston so that the pilot spool moves with the one piston and shifting ofthe control spool is responsive to the position of the one piston.

It is an object in one embodiment of the invention to reduce the overallsize of the valving arrangement and to eliminate conduits extendingbetween the two valves by forming the pilot valve as a spool slidablytelescoped with the spool of the control valve.

The invention also resides in providing cylinders of different volume sothat the larger cylinder can serve as a reservoir for the hydraulicfluid in the secondary circuit to accommodate volume change in thehydraulic fluid in the secondary circuit while the piston in the largercylinder moves through a stroke equivalent to the stroke of the pistonin the smaller cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial schematic view ofa hydraulic system and shows an enlarged schematic view of an isolatorembodying the novel features of the present invention.

FIG. 2 is a fragmentary schematic view of the control and pilot valveand shows both cylinders and pistons.

FIG. 3 is a fragmentary perspective view of a second embodiment of thevalving arrangement.

FIG. 4 is a cross-sectional view of the valving arrangement of FIG. 3.

FIG. 5 is a view similar. to FIG. 4 and shows parts in a moved position.

FIG. 6 is a view similar to FIG. 4 and shows parts in another movedposition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in thedrawings for purposes of illustration the invention is embodied in afluid isolator 10 (FIG. I which connects a high-pressure fluid line 11and a low-pressure fluid line 12 to a load or operator 13 for actuatingthe operator. A plurality of operators are connected to the high and lowpressure lines through individual isolators which isolate the operatorfrom the pressure lines so that, if a leak should occur in the fluidcircuit of the operator, the isolator will prevent the loss of pressurein the high-pressure line thus enabling the highpressure line tocontinue to service the other operators.

Herein, the isolator 10 comprises a primary fluid circuit I4 which isconnected to the high and low-pressure fluid lines 11 and 12 and asecondary fluid circuit 15 which is connected to the operator l3 and isfilled with a hydraulic fluid such as oil. In this instance, the highpressure is approximately 3,000 p.s.i., and the low pressure isapproximately p.s.i. The two circuits are connected together so thatpower but not fluid from the primary circuit is transferred to thesecondary circuit to actuate the operator. For this purpose, first andsecond cylinders 17 and 18 each communicate at one end, the primary end,with the primary circuit and at the other end, the secondary end, withthe secondary circuit. To prevent the interchange of fluid through thecylinders and to transmit power between the circuits, first and secondfree-floating pistons 19 and 20 are slidably mounted in the cylinders,one piston per cylinder.

To drive the pistons 19 and 20 alternately through power strokes, avalving arrangement 21 (FIG. 2) in the primary circuit l4 directspressure fluid from the high-pressure line 11 alternately into theprimary ends of the cylinders 17 and 18. These alternating power strokescause an alternating flow of oil in the secondary circuit 15, and thisflow is transformed into a unidirectional flow to pass through andactuate the operator 13. As shown in FIGS. 1 and 3, four check valves22, 23, 24 and 25 are arranged in the secondary circuit to transform thealternating flow to unidirectional flow. When the first piston 19 ispositioned to begin its power stroke, the second piston 20 is positionedto begin its return stroke (FIG. 1). High-pressure fluid is directed tothe primary and of the first cylinder 17 to drive the first pistonthrough its power stoke thus causing a positive flow of oil from thefirst cylinder and into the secondary circuit. This flow is directedthrough the check valve 24 to the intake line 27 of the operator. Flowinto the operator causes low-pressure exhaust flow out of the operatorthrough a low-pressure line 28, and this flow is directed through thecheck valve 22 to the secondary end of the second cylinder 18 thuspushing the second piston 20 through its return stroke. When the firstpiston reaches the end of its power stroke, the valving arrangement 21is operable to direct the high-pressure fluid to the primary end of thesecond cylinder to drive the second piston through its power stroke toforce oil from the second cylinder and through the check valve 23 andinto the intake line 27, the exhaust flow from the operator passingthrough the check valve 25 to move the first piston through its returnstroke. Thus the alternating flow from the cylinders is transformed intounidirectional flow through the intake line and to the operator. Withthis arrangement, the secondary circuit is a closed circuit isolatedfrom the primary circuit.

In the valving arrangement 21, a valve member 30 (FIG. 2) is shiftedbetween a first position and second position to direct the pressurefluid first to one cylinder and then the other. The shifting of thevalve member is arranged so that the pistons 19 and 20 move throughequivalent power strokes.

The present invention contemplates the provision of a novel valvingarrangement 21 which results in positive shifting of the valve member 30between its two operating positions to provide quiet, smooth andpositive functioning of the isolator during normal operation and which,when a leak occurs in the secondary circuit stops the valve member inone of the operating positions and holds it there in a quiescent stateto prevent nonuseful expenditure of energy and damage to the parts andto eliminate noise of moving parts, Further the arrangement of the novelvalving permits the use of either a hydraulic fluid or a compressiblegas in the pressure lines 11 ad 13 and in the primary circuit 14, Tothese ends, the valve member 30 is a part of a control valve 31 and isshifted from one operating position to the other under the control of apilot valve 32 which is positively actuated by one of the pistons 19 and20, herein the piston 19. The pilot valve causes the valve member toshift to one operating position at the end of the power stroke of thepiston 19 and to the other operating position at the end of the returnstroke of the piston. Thus, should a leak occur in the secondary circuit15, both pistons will come to rest, and preferably will bottom, and themember will be locked in one operating position or be shifted to theother operating position to be locked in that position.

in the embodiment of FIG. 2, the control valve 31 comprises a housing 33with the control spool 30 being mounted in a chamber 34 in the housingfor endwise sliding. Two intake ports 36 and 37 connect the oppositeends of the chamber to a line 38 leading to the high-pressure line 11for the admission of high-pressure fluid into the chamber. In thisinstance, oil is used in the lines 11 and 12 and in the primary andsecondary circuits l4 and 15. The low-pressure line 12 is connected by aline 39 to a port 40 leading into the center of the chamber, and ports41 and 42 connect the chamber with the primary ends of the cylinders 17and 18 through lines 43 and 44 so that highpressure oil may be directedto the cylinders and low-pressure oil may flow from the cylinders. FromFIG. 2, it will be observed that the control spool comprises a smalldiameter shaft 45 which is longer than the chamber but shorter than thehousing, and the opposite end portions of the shaft are slidably mountedin a pistonlike manner in secondary chambers 46 and 47 in the endportions of the housing. To direct the flow of high-pressure andlow-pressure oil through the chamber 34 and to prevent mixing of thetwo, tow lands 48 and 49 are formed on the shaft.

The control spool 30 is shifted between the first position shown in FIG.2, and a second position (not shown) to direct the high-pressure oilfirst to one cylinder then the other. When the control spool is in thefirst position the port 37 communicates with the port 41 to direct highpressure oil to the primary end of the first cylinder 17, and the secondcylinder 18 is connected to the low-pressure line 34 through ports 40and 42. To direct the flow are high-pressure oil to the second cylinder,the control spool is shifted downwardly until the lower end (FIG. 2) ofthe shaft engages the bottom of its secondary chamber 46. This movementslides the lands 48 and 49 in the chamber 34 so that the port 36communicates with the port 42 in the chamber 34 so that the port 36communicates with the port 42 to direct the high-pressure oil to theprimary end of the second cylinder 18 while connecting the firstcylinder with the low-pressure line through ports 40 and 41. It will beobserved that in neither position are the intake ports 36 and 37 blockedby the lands thus maintaining generally equal pressure in the oppositeend portions of the chamber so that only a small amount of force isneeded to shift the control spool.

To shift the control spool 30, the pilot valve 32 is operable to directhigh-pressure oil alternately to the secondary chambers 46 and 47 tocause the end portions of the shaft 45 to act as pistons under pressure.In this instance, the pilot valve comprises a housing 50 and a pilotspool 51 slidably mounted in a chamber 52 formed in the housing. A line53 extends between ports 54 and 55 in the upper and lower ends of thehousing and a port 56 in the lower end of the control housing 33 toconnect the chamber 52 with the lower end of the secondary chamber 46,the port 56 being of smaller diameter than the secondary chamber. Theupper end of the secondary chamber 47 communicates with the pilotchamber 52 through a port 58 in the pilot housing and a port 59, similarto the port 56, in the upper end of the control housing, the ports 58and 59 being 5 joined by a line 60. A line 61 connects a port 62 to thehighpressure line 38, ad a line 63 connects a port 64 to the lowpressureline 39. As shown in F IG. 2, the pilot spool comprises a long shaft 65which extends through the bottom of the housing 50, a short land 66 onthe upper end of the shaft. and a long land 67 spaced downwardly on theshaft from the short land. To operate the control valve, the pilot spoolis slid up and down in the pilot housing to direct the high-pressure oilalternately to one of the ports 56 and 59 while connecting the other tothe low-Pressure line. In order that the pilot valve moves with thepiston 19 thereby insuring that the spool 30 is held in a predeterminedfixed position when a leak occurs in the secondary circuit 15, the lowerend of the shaft 65 is rigidly connected to the piston 19 so that thepilot spool slides up and down as the first piston moves through itspower and return strokes.

For a summary of the operation of the valves 31 and 32, assume that thefirst piston 19 is at the primary end of the first cylinder 17 and thesecond piston 20 is ready to begin its return stroke. As shown in FIG.2, the high-pressure oil is directed by the pilot valve 32 to the lowerend of the secondary chamber 46, and the control spool 30 is in thefirst position directing the high-pressure oil to the primary end of thefirst cylinder and connecting the second cylinder 18 to the lowpressureline 39. As the first piston moves through its power stroke, the secondpiston moves through its return stroke, and the pilot spool slides downin the pilot chamber 52. When the first piston reaches the secondary endof its cylinder, the pilot spool is located so that the high-pressureoil is disconnected from the secondary chamber 46 and is connected tothe secondary chamber 47, the high-pressure oil passing through ports 62and 58 and through the chamber 52 between lands 66 and 67. The resultingpressure of the oil against the upper end of the control shaft 45 forcesthe control spool to shift and thus to disconnect the high-pressure oilfrom the first cylinder and to connect the high-pressure oil throughports 36 and 42 to the second cylinder in which the second piston hascompleted its return stroke. As a result'of the shift in thehighpressure oil, the second piston is moved through its power strokethus moving the first piston through its return stroke. As this occurs,the pilot spool slides upwardly in the chamber 52, and when the firstpiston nears the end of its return stroke the lower end of the land 67passes by and uncovers the port 62 to direct the high-pressure oilthrough the port 55 to the port 56 to push against the lower end of theshaft 45 to shift the control spool 30 into the position shown in FIG. 2ready to begin another cycle of operation.

If an oil leak should occur in the secondary circuit 15, the pistons 19and 20 will end up at the secondary ends of the cylinders 17 and 18, andthe control spool 30 will be locked into its second position. If theleak occurs during the power stroke of the first piston 17, the latterwill continue to the end of its power stroke to pull the pilot spool 51and shift the control spool to direct high-pressure oil into the secondcylinder 18 to drive the second piston 20 through its power stroke. Oncethe leak occurs,' no low-pressure oil will flow into the secondary endof either cylinder. Thus, neither piston would be returned. With thefirst piston at the secondary end of the first cylinder and no lowpressure oil available to push the piston through a return stroke, thepilot spool will remain in a position to direct high-pressure oil intothe secondary chamber 47 thus locking the control spool in its secondposition. If the leak occurs during the power stroke of the secondpiston, the latter will be driven to the secondary end of its cylinder.Because no low-pressure oil will be directed into the secondary end ofthe first cylinder 17, the low-pressure oil from the first circuit, theoil being under approximately l00 p.s.i. will push the first piston tothe secondary end of its cylinder thus pulling the pilot spool down tolock the control spool in its second position in the manner describedabove.

In accordance with another aspect of the invention, the second cylinder18 is utilized to accommodate the changing volume of the oil in thesecondary circuit due to thermal expansion of the fluid and the effectof using an unbalanced operator 13 thereby eliminating the need for aseparate reservoir in the secondary circuit. To these ends, the volumeof the second cylinder is greater than the volume of the first cylinderand the sliding of the pilot spool 51 is controlled exclusively by thefirst piston 19 so that, while the first piston normally moves through astroke which extends from end to end of the first cylinder 17, thesecond piston in the larger cylinder will normally move through a strokewhich is shorter than the full distance from end to end of the secondcylinder.

While it is not necessary, both cylinders 17 and 18 have, in thisinstance, generally equal diameters wi the length of the second cylinder18 being greater than that of the first cylinder 17 to effect thegreater volume of the second cylinder. The piston 20 is free-floatingwithin the second cylinder and thus may move through its power or returnstroke anywhere within the length of the second cylinder. When the oilis cooled, its volume decreases, and the second piston moves through itsstrokes in the secondary end portion of the cylinder. When the oil isheated, its volume increases to fill a portion of the second cylinder,and the second piston moves through its strokes in the primary endportion of the cylinder. The same action of the piston 20 occurs when anunbalanced operator [3 is used. The stroke that the second piston movesthrough, barring a leak, is always shorter than the length of itscylinder because the shifting of the control spool 30 is exclusivelycontrolled by the first piston 19 through the connection of the shaft 65of the pilot spool 51 to the first piston, and thus the second pistonmoves through strokes correlated to the length of the stroke of thefirst piston.

A modified valving arrangement 21' embodying novel features of thepresent invention is shown in FIG. 3 through 6 in which partscorresponding to those of the valving arrangement 21 are indicated bythe same but primed reference numerals. Like the valving arrangement 21,the valving arrangement 21' includes a control valve housing 33' (FIG.4), a control spool 30' slidably mounted in a chamber 34' in thehousing, and a pilot valve spool 51 with a shaft 65' which is connectedto the first piston 19. In accordance with this aspect of the invention,the pilot spool 51' is slidably telescoped with the control spool 30 andis concentric with the control spool and the control valve housing 33'.With this arrangement, all the interconnecting passages are fabricatedin the parts themselves to eliminate all the small diameter lines andlong passages. Additionally, a separate pilot valve housing is notrequired.

As best shown in FIG. 4, the control valve housing 33' forms the chamber34 in which the control spool 30' is slidably mounted; and a number ofports connect the chamber with lines leading to the first and secondcylinders 17 and 18 and to the high and low-pressure lines 38 and 39.Thus, a line 43' through a port 41' in the lower end portion of thehousing connects the chamber with the primary end of the first cylinder17, and a line 44' through a port 42' in the upper end portion of thehousing connects the chamber with the primary end of the second cylinder18. The low pressure line 39 is connected to the chamber by lines 70 and71 which are connected to upper and lower low pressure ports 72 and 73in the opposite end portions of the housing. To introduce high-pressureoil into the chamber, the high-pressure line 38 is connected to a port74.

As shown in progressive steps in FIGS. 4 to 6, the control spool 30 isshifted between a first position (FIG. 4) and a second position (FIG. 6)to direct the high-pressure oil first to one cylinder then the other.The control spool is cylindrical with a body 75 of smaller diameter thanthe diameter of the chamber 34' and with lands 76 and 77 at oppositeends of the body to divide the chamber 34' and with lands 76 and 77 atopposite ends of the body to divide the chamber and block the flow ofoil between various ones of the ports. When the control spool is in itsfirst position (FIG. 4), the high-pressure port 74 communicates with theport 41 to direct high pressure oil to the first cylinder 17, the oilpassing through the chamber around the body of the spool and between thelands. In this position the upper low-pressure port 72 communicates withthe port 42' to connect the second cylinder to the low-pressure line 39.When the control spool is in its second position (FIG. 6), thehigh-pressure port 74 communicates with the port 42' to directhigh-pressure oil to the second cylinder and the lower low-pressure port73 communicates with the port 41' to connect the first cylinder to thelow-pressure line.

As with the first embodiment, the shifting of the control spool 30' iscontrolled by the shifting of the pilot spool 51 in response to themovement of the first piston 19. In this instance the pilot spool 51 isan elongated cylindrical stem 65 with a single land 79 formed thereon.The stem is connected at its lower end to the upper surface of the firstpiston 19 and extends upwardly therefrom onto the control housing 33'through a hole 80 in the bottom of the housing. To prevent oil fromleaking out the hole, a seal 81 is placed in the bottom of the chamber34'. As shown in FIGS. 4 through 6, the upper portion of the stemextends through an axial passage 82 in the control spool 30 with theland 79 being positioned within the passage. Bushings 83 and 84 at theupper and lower ends of the passage seal around the stem to form achamber of the passage. To allow high-pressure oil into and out of thepassage, a port 85 is formed through the wall of the control spool atthe vertical center of the spool and, to vent the passage to lowpressure, two slots 86 and 87 are milled into the stem. One slot 86extends axially from just above land 79 upwardly while the other 87extends axially downwardly from just below the land. The stem and thecontrol housing are dimensioned such that, when the first piston 19 ispositioned to begin its power stroke, the top of the stem is just belowthe top of the housing (FIG. 4) and, when the first piston completes itspower stroke, the top of the stem is just above the bottom of the upperlow-pressure port 72 (FIG. 6).

As the first piston 19 moves through its power and return strokes, thesliding of the pilot spool 51' relative to the control spool 30' shiftsthe bias of the high-pressure oil in the control spool to cause thelatter to shift between the first and second positions. In followingthrough a cycle of operation, assume that the first piston 19 is poisedto begin its power stroke and the control spool is positioned in itsfirst position (FIG. 4) directing the high-pressure oil to the firstcylinder 17. The high-pressure oil also fills the passage 82 below theland 79, the oil having flowed into the passage through the port 85. Asthe first piston moves through its power stroke, the land 79 movesdownwardly in the passage thus forcing the high-pressure oil out of thepassage through the port 85, and low-pressure oil flows into the passageabove the land, the oil flowing through the slot 86. As shown in FIG. 5,the upper slot 86 is of such a length that, when the land moves past theport 85, the upper end of the upper slot moves past the bushing 83 tobreak the communication of the passage with the low-pressure fluid. Thelower slot 87 is of such a length that, when the land 79 movesdownwardly past the port 85, the lower end of the lower slot moves pastthe bushing 84 to establish communica tion between the portion ofpassage below the land and the low-pressure through the port 73. Thuswhen the land moves downwardly past the port 85, the upper portion ofthe passage fills with high-pressure oil and the oil in the lowerportion of the passage becomes low-pressure oil. This occurs as thefirst piston reaches the end of its power stroke, and the high pressureabove the land, in effect pushes against the bearing 83 and forces thecontrol spool to shift, as shown in FIG. 6, to its second position.

The shifting of the control spool 30' to its second position causes thehigh-pressure oil to be directed to the second cylinder 18 and causesthe first cylinder 17 to be connected to the low pressure port 73. Theoperation of the pilot spool 51' to shift the control spool from thesecond position back to the first position is similar to that forshifting the control spool from the first position to the second. As thefirst piston 19 moves through its return stroke, the stem 65' movesupwardly,

and the land 79 forces the high-pressure oil out of the upper portion ofthe passage 82 through the port 85 with the lower portion of the passagefiling with low-pressure oil through the lower slot 87. As the landpasses the port 85, the lower end of the lower slot passes into thebushing 84 thus disconnecting the lower portion of the passage from thelow-pressure port 73, and the upper end portion of the upper slot 86passe through the bushing 83 to connect the upper portion of the passagewith the low-pressure port 72. The land passes the port 85 as the firstpiston reaches the end of its return stroke. When this occurs, the lowerportion of the passage is filled with high-pressure oil which flows inthrough the port 85, and the resulting pressure against the bearing 84causes the control spool to shift back to its first position thuscompleting a full cycle of operation. if a leak should occur in thesecondary circuit 15, both pistons would end up at the bottoms of theirrespective cylinders, as described above in connection with the firstembodiment of the valving arrangement, and the control spool 30 would belocked into its second position.

From the above, it will be observed that the provision of the pilotspool 51, 51' which is controlled by the movement of only the firstpiston 19 to control the shifting of the control spool 30, 30 is aparticularly advantageous arrangement. With this arrangement, should aleak occur in the secondary circuit 15, the control spool will be lockedinto its second position to prevent waste of energy and possible damageto the valving arrangement caused by indiscriminately moving parts,Also, the isolator 10 is operable whether the first circuit 14 is filledwith hydraulic fluid or a gas. Another advantageous arrangement is theformation of the second cylinder 18 larger than the first cylinder 17 toact as a reservoir to accommodate changes in the volume of the hydraulicfluid in the second circuit. To conserve space and eliminate many parts,the valving arrangement 21' of the second embodiment comprises a pilotspool 5l-which is concentric with and slides through the control spool30.

We claim as our invention:

1. in a fluid isolator adapted to be connected between a high-pressurefluid line and a low-pressure line for operating one of a plurality offluid loads from a common source of highpressure fluid, the combinationof, a primary fluid circuit adapted to be connected between thehigh-pressure line and the low-pressure line, a secondary fluid circuitadapted to be connected to the one load, means connected between saidcircuits for transmitting power from said primary circuit to saidsecondary circuit for operation of the one load, said means comprising afirst cylinder, 51 first free-floating piston in said second cylinder, asecond cylinder, a second free-floating piston in said second cylinder,a first end of each cylinder communicating with said primary circuit andthe second end of each cylinder communicating with said secondarycircuit, control means in said primary circuit for alternately directinghigh-pressure fluid from the high-pressure line to said first ends ofsaid cylinders to drive said pistons through power strokes toward saidsecond ends to cause an alternating flow of high-pressure fluid in saidsecondary circuit, means in said secondary circuit for transforming saidalternating flow to a unidirectional flow through the load whiledirecting the lowpressure fluid from the load alternately to the secondends of the cylinders to return one piston toward the first end of itscylinder as the other piston moves through its power stroke, saidcontrol means comprising a control valve connected in said primarycircuit for directing pressure fluid to said first end of either of saidcylinders while directing low-pressure fluid from the first end of theother said cylinder to the low-pressure line, a pilot valve connected tosaid control valve and operable to actuate said control valve to changethe flow of high-pressure fluid and low-pressure fluid from one cylinderto the other to cause the alternating power strokes of said pistons, andmeans connecting said pilot valve and first piston for operating saidpilot valve in response to movement of said first piston between theends of said first cylinder whereby if a fluid leak occurs in saidsecondary circuit, the valves will come to rest in fixed positions toallow the pressure source to continue to be used to actuate theremaining loads.

2. The fluid isolator of claim I in which said means connected to saidpilot valve is a rigid connection between the pilot valve and said firstpiston.

3. The fluid isolator of claim 1 in which secondary circuit is filledwith a liquid.

4. The fluid isolator of claim 3 in which said second cylinder has alarger volume than said first cylinder so that said second cylinderserves as a resevoir to accommodate volume changes in the liquid in saidsecondary circuit while still allowing said second piston to movethrough strokes equivalent to the strokes of said first piston.

5. in a fluid isolator adapted to be connected between a high-pressurefluid line and low-pressure fluid line for actuating one of a pluralityof fluid operators from a common source of high-pressure fluid, thecombination of, a primary fluid cir cuit adapted to be connected betweenthe high-pressure line and the low-pressure line, a secondary fluidcircuit adapted to be connected to the one operator, means connectedbetween said circuits for transmitting power from said primary circuitto said secondary circuit for actuation of the one operator, said meanscomprising a first cylinder, a first free-floating piston in saidcylinder, a second cylinder, a second free-floating piston in saidsecond cylinder, a first end of each cylinder communicating with saidprimary circuit and the second end of each cylinder communicating withsaid secondary circuit, control means in said primary circuit foralternately directing high-pressure fluid to said first ends of saidcylinders to drive said pistons through power strokes toward said secondends to cause in said secondary circuit a flow of pressure fluidoperable to activate the one operator while returning one piston towardthe first end of its cylinder as the other piston moves through itspower stroke, said control means comprising a control valve connected insaid primary circuit and movable between first and second positions,said control valve being operable in said first position to directhigh-pressure fluid to said first end of said first cylinder and connectsaid second cylinder to said low-pressure line and operable in saidsecond position to direct high-pressure fluid to said first end of saidsecond cylinder while connecting said first cylinder to saidlow-pressure line, a pilot valve connected to said control valve andoperable, when moved in one direction, to shift said control valve tosaid first position, and when moved in the opposite direction to shiftthe control valve to said second position and thereby to cause thealternating power strokes of said piston and means connecting said pilotvalve and said first piston to cause the pilot valve to move back andforth with said first piston whereby, if a fluid leak occurs in saidsecondary circuit, both pistons will move to said second ends of theircylinders and said control valve will come to rest in one of saidpositions to allow the pressure source to continue to be used to actuatethe remaining operators.

6. The fluid isolator of claim 5 in which the secondary circuit isfilled with a liquid pressure fluid.

7. The fluid isolator of claim 6 in which said second cylinder has alarger volume than said first cylinder to accommodate the liquid fillingsaid secondary circuit as said liquid expands or contracts while stillallowing said second piston to move through strokes equivalent to thestrokes of said first piston.

8. The fluid isolator of claim 6 in which the pressure fluid passingthrough the primary circuit is a liquid.

9. The fluid isolator of claim 5 in which said control valve comprises ahousing and a control spool movable within said housing between saidfirst and second positions, said pilot valve comprises a second housingand a pilot spool movable within said second housing in said directions,and conduits extending between said pilot valve and said control valveto convey high-pressure fluid from said pilot valve to said controlvalve.

10. The fluid isolator of claim 9 in which said means connecting saidpilot valve and said first piston comprises a shaft connected at one endto one end of said pilot spool and connected at its other end to saidfirst piston so that movement of said first piston moves said pilotspool.

11. The fluid isolator of claim in which said control valve comprises ahousing and a control spool slidable within said housing between saidpositions and said pilot valve is formed concentric with said controlvalve and comprises a pilot spool slidably telescoped with said controlspool whereby movement of said pilot spool in said directions causessaid control spool to slide between said positions.

12. The fluid isolator of claim 11 in which said control spool has apassage formed therethrough and said pilot spool is slidably telescopedwithin said control spool.

13. The fluid isolator of claim 11 in which said means connecting saidpilot valve and said first piston comprises a shaft connected at one endto said first piston and at its other end to said pilot spool.

14. In a hydraulic isolator connected between a high-pressure hydraulicfluid line and a low-pressure hydraulic fluid line for actuating one ofa plurality of fluid operators from a common source of high-pressurehydraulic fluid, the combination of, a primary hydraulic circuitconnected between the highpressure line and the low-pressure line, asecondary hydraulic circuit connected to the one operator and filledwith hydraulic fluid, means connected between said circuits fortransmitting power from said primary circuit to said secondary circuitfor actuation of the one operator, said means comprising a firstcylinder, at first free-floating piston in said cylinder, a secondcylinder, a second free-floating piston in said second cylinder, a firstend of each cylinder communicating with said primary circuit and thesecond end of each cylinder communicating with said secondary circuit,control means in said primary circuit for alternately directlyhigh-pressure fluid to said first ends of said cylinders to drive saidpistons through power strokes toward said second ends to cause analternating flow of high-pressure fluid in said secondary circuit, meansin said secondary circuit for transforming said alternating flow to aunidirectional flow through the operator while directing thelow-pressure hydraulic fluid from the operator alternately to the secondends of the cylinders to push one piston toward said first end of itscylinder as the other piston moves through its power stroke, saidcontrol means comprising a control valve having a housing and a controlspool with a passage therethrough, said spool being slidable in saidhousing between first and second positions, said control valve beingoperable when said spool is in said first position to directhighpressure fluid from the high-pressure line to said first end of saidfirst cylinder and to connect said first end of said second cylinder tothe low-pressure line and operable when said spool is in said secondposition to direct high-pressure fluid to said first end of said secondcylinder while connecting said first end of said first cylinder to thelow-pressure line, a pilot valve comprising a pilot spool slidablymounted within said passage of said control spool, said pilot valvebeing operable, when said pilot spool is moved in one direction, toshift said control spool to said first position and, when said pilotspool is moved in the opposite direction, to shift the control spool tosaid second position thereby to cause the alternating power strokes ofsaid piston, and a shaft extending between and connected to said pilotspool and said first piston to cause the pilot spool to move back andforth with the strokes of said first piston whereby, if a hydraulicfluid leak occurs in said secondary circuit, each piston will move tosaid second end of its cylinder and said control spool will be locked inone of said positions to allow the pressure source to continue to beused to actuate the remaining operators.

* i l t i

1. In a fluid isolator adapted to be connected between a highpressurefluid line and a low-pressure line for operating one of a plurality offluid loads from a common source of high-pressure fluid, the combinationof, a primary fluid circuit adapted to be connected between thehigh-pressure line and the low-pressure line, a secondary fluid circuitadapted to be connected to the one load, means connected between saidcircuits for transmitting power from said primary circuit to saidsecondary circuit for operation of the one load, said means comprising afirst cylinder, a first free-floating piston in said cylinder, a secondcylinder, a second free-floating piston in said second cylinder, a firstend of each cylinder communicating with said primary circuit and thesecond end of each cylinder communicating with said secondary circuit,control means in said primary circuit for alternately directinghigh-pressure fluid from the high-pressure line to said first ends ofsaid cylinders to drive said pistons through power strokes toward saidsecond ends to cause an alternating flow of high-pressure fluid in saidsecondary circuit, means in said secondary circuit for transforming saidalternating flow to a unidirectional flow through the load whiledirecting the low-pressure fluid from the load alternately to the secondends of the cylinders to return one piston toward the first end of itscylinder as the other piston moves through its power stroke, saidcontrol means comprising a control valve connected in said primarycircuit for directing pressure fluid to said first end of either of saidcylinders while directing lowpressure fluid from the first end of theother said cylinder to the low-pressure line, a pilot valve connected tosaid control valve and operable to actuate said control valve to changethe flow of high-pressure fluid and low-pressure fluid from one cylinderto the other to cause the alternating power strokes of said pistons, andmeans connecting said pilot valve and first piston for operating saidpilot valve in response to movement of said first piston between theends of said first cylinder whereby if a fluid leak occurs in saidsecondary circuit, the valves will come to rest in fixed positions toallow the pressure source to continue to be used to actuate theremaining loads.
 2. The fluid isolator of claim 1 in which said meansconnected to said pilot valve is a rigid connection between the pilotvalve and said first piston.
 3. The fluid isolator of claim 1 in whichsecondary circuit is filled with a liquid.
 4. The fluid isolator ofclaim 3 in which said second cylinder has a larger volume than saidfirst cylinder so that said second cylinder serves as a resevoir toaccommodate volume changes in the liquid in said secondary circuit whilestill allowing said second piston to move through strokes equivalent tothe strokes of said first piston.
 5. In a fluid isolator adapted to beconnected between a high-pressure fluid line and a low-pressure fluidline for actuating one of a plurality of fluid operators from a commonsource of high-pressure fluid, the combination of, a primary fluidcircuit adapted to be connected between the high-pressure line and thelow-pressure line, a secondary fluid circuit adapted to be connected tothe one operator, means connected between said circuits for transmittingpower from said primary circuit to said secondary circuit for actuationof the one operator, said means comprising a first cylinder, a firstfree-floating piston in said cylinder, a second cylinder, a secondfree-floating piston in said second cylinder, a first end of eachcylinder communicating with said primary circuit and the second end ofeach cylinder communicating with said secondary circuit, control meansin said primary circuit for alternately directing high-pressure fluid tosaid first ends of said cylinders to drive said pistons through powerstrokes toward said second ends to cause in said secondary circuit aflow of pressure fluid operable to activate the one operator whilereturning one piston toward the first end of its cylinder as the otherpiston moves through its power stroke, said control means comprising acontrol valve connected in said primary circuit and movable betweenfirst and second positions, said control valve being operable in saidfirst position to direct high-pressure fluid to said first end of saidfirst cylinder and connect said second cylinder to said low-pressureline and operable in said second position to direct high-pressure fluidto said first end of said second cylinder while connecting said firstcylinder to said low-pressure line, a pilot valve connected to saidcontrol valve and operable, when moved in one direction, to shift saidcontrol valve to said first position, and when moved in the oppositedirection, to shift the control valve to said second position andthereby to cause the alternating power strokes of said pistons, andmeans connecting said pilot valve and said first piston to cause thepilot valve to move back and forth with said first piston whereby, if afluid leak occurs in said secondary circuit, both pistons will move tosaid second ends of their cylinders and said control valve will come torest in one of said positions to allow the pressure source to continueto be used to actuate the remaining operators.
 6. The fluid isolator ofclaim 5 in which the secondary circuit is filled with a liquid pressurefluid.
 7. The fluid isolator of claim 6 in which said second cylinderhas a larger volume than said first cylinder to accommodate the liquidfilling said secondary circuit as said liquid expands or contracts whilestill allowing said second piston to move through strokes equivalent tothe strokes of said first piston.
 8. The fluid isolator of claim 6 inwhich the pressure fluid passing through the primary circuit is aliquid.
 9. The fluid isolator of claim 5 in which said control valvecomprises a housing and a control spool movable within said housingbetween said first and second positions, said pilot valve comprises asecond housing and a pilot spool movable within said second housing insaid directions, and conduits extending between said pilot valve andsaid control valve to convey high-pressure fluid from said pilot valveto said control valve.
 10. The fluid isolator of claim 9 in which saidmeans connecting said pilot valve and said first piston comprises ashaft connected at one end to one end of said pilot spool and connectedat its other end to said first piston so that movement of said firstpiston moves said pilot spool.
 11. The fluid isolator of claim 5 inwhich said control valve comprises a housing and a control spoolslidable within said housing between said positions and said pilot valveis formed concentric with said control valve and comprises a pilot spoolslidably telescoped with said control spool whereby movement of saidpilot spool in said directions causes said control spool to slidebetween said positions.
 12. The fluid isolator of claim 11 in which saidcontrol spool has a passage formed therethrough and said pilot spool isslidably telescoped within said control spool.
 13. The fluid isolator ofclaim 11 in which said means connecting said pilot valve and said firstpiston comprises a shaft connected at one end to said first piston andat its other end to said pilot spool.
 14. In a hydraulic isolatorconnected between a high-pressure hydraulic fluid line and alow-pressure hydraulic fluid line for actuating one of a plurality offluid operators from a common source of high-pressure hydraulic fluid,the combination of, a primary hydraulic circuit connected between thehigh-pressure line and the low-pressure line, a secondary hydrauliccircuit connected to the one operator and filled with hydraulic fluid,means connected between said circuits for transmitting power from saidprimary circuit to said secondary circuit for actuation of the oneoperator, said means comprising a first cylinder, a first free-floatingpiston in said cylinder, a second cylinder, a second free-floatingpiston in said second cylinder, a first end of each cylindercommunicating with said primary circuit and the second end of eachcylinder communicating with said secondary circuit, control means insaid primary circuit for alternately directing high-pressure fluid tosaid first ends of said cylinders to drive said pistons through powerstrokes toward said second ends to cause an alternating flow ofhigh-pressure fluid in said secondary circuit, means in said secondarycircuit for transforming said alternating flow to a unidirectional flowthrough the operator while directing the low-pressure hydraulic fluidfrom the operator alternately to the second ends of the cylinders topush one piston toward said first end of its cylinder as the otherpiston moves through its power stroke, said control means comprising acontrol valve having a housing and a control spool with a passagetherethrough, said spool being slidable in said housing between firstand second positions, said control valve being operable when said spoolis in said first position to direct high-pressure fluid from thehigh-pressure line to said first end of said first cylinder and toconnect said first end of said second cylinder to the low-pressure lineand operable when said spool is in said second position to directhigh-pressure fluid to said first end of said second cylinder whileconnecting said first end of said first cylinder to the low-pressureline, a pilot valve comprising a pilot spool slidably mounted withinsaid passage of said control spool, said pilot valve being operable,when said pilot spool is moved in one direction, to shift said controlspool to said first position and, when said pilot spool is moved in theopposite direction, to shift the control spool to said second positionthereby to cause the alternating power strokes of said pistons, and ashaft extending between and connected to said pilot spool and said firstpiston to cause the pilot spool to move back and forth with the strokesof said first piston whereby, if a hydraulIc fluid leak occurs in saidsecondary circuit, each piston will move to said second end of itscylinder and said control spool will be locked in one of said positionsto allow the pressure source to continue to be used to actuate theremaining operators.